Laminated tube structure



July 24, 1956 w. F. STAHL LAMINATED TUBE smucruas Filed April 21, 1953IN V EN TOR: fldmfib za/, B Y M, kZzfizt y w,

ATTORNEYS.

LAMINATED TUBE STRUCTURE William F. Stahl, Kenilworth, Ill. ApplicationApril 21, 1953, Serial No. 350,083

8 Claims. (Cl. 138-76) This invention relates to laminated tubes, andmore particularly to laminated tubes wherein at least a portion of thelaminations are formed of a material that cannot be secured together bypresently-known means such as glue, adhesives, heat sealing, etc. Thelaminated tubes may be cylindrical, square, rectangular, or of anydesired cross-sectional configuration. Such tubes have numerous usesand, for example, may be employed in numerous electrical applications.Exemplary of an electrical application is the use of the tubes as basesor forms for coil windings, transformer windings, etc.

There are two widely used methods for forming lamihated tubes. One ofthese methods is, spirally winding separate layers or strips of thematerial forming the tube one upon another to provide the laminations.This type of operation is continuous and very rapid and tubes formed bythis method are frequently wound at a speed of approximately 80 feet perminute. The second method is to employ a wide band of material and coilit so that the convolutions he one upon another and form a cylindricaltube. This is not a continuous operation in that when a sufficientnumber of turns are taken to provide the desired wall thickness the wideband or web of material must be severed and a second winding operationmust then be started before another tube may be formed. In this type ofoperation the length of the tube is limited by the width of the startingweb or band. The rate at which tubes may be formed in the convolutewinding operation is approximately 2 feet per 10 minutes. It isapparent, then, that spiral winding of tubes is the most desirable froma commercial point of view in that it is by far the less expensive andmost rapid.

There are a number of materials, particularly in the plastics, that haveexcellent dielectric and insulating properties and could be used verydesirably in the electrical field Where members having high dielectricand insulating properties are needed. A number of such needs involve theuse of tubular members, as for example the forms for coil windings, etc.With such materials it is a simple matter to provide just the rightdielectric strength needed by providing the number of layers of thematerial required to yield the specific dielectric capacity. Thedifificulty has been, however, that a number of these desirablematerials cannot be secured to themselves by known means so that arigid, unitary structure could be provided. It has been customary toform tubes of such materials by cylindrically winding webs of thematerial and then securing the laminations together by mechanical meanssuch as by rivets or bolts, etc. The reason this method of tubeformation has been employed is that it has heretofore been believedimpossible to form tubular members of such material by the usual spiralwinding method because spiral winding of. a number of laminations oneupon another requires that each layer or lamination be rigidly joined tothe one before and that it covers. Spiral winding could not, then, beused where the material forming the laminations could not be secured toeach other by adhesives,

States Patent ice or by heat sealing or other known means. I have discovered a structure that permits the formation of spirallywoundlaminated tubes and in which at least some of the laminations are formedof a material that cannot be secured to itself or to other materials bypresentlyknown means.

My laminated tubular structure is also desirable for another reason. Inspiral winding operations wherein laminated tubes are formed, stressesare frequently built up in the tube during the forming thereof that tendto distort the same, though initially the stresses are overcome by theadhesion of one spiral layer to another and the formation thereby of arigid, integrated tube structure. However, when the tube is subsequentlyemployed as a bobbin core and electric conductors are wound thereon toform coils, etc., the heat developed by the current flowing through theconductor tends to amplify the latent stresses and cause core distortionwhich is undesirable. The same distortion condition arises when thelaminated tubes or cores are treated to obtain certain mechanical orelectrical characteristics, as for example resin impregnation of thelaminations. Impregnation treatments are generally harsh and bring outthe unequal stresses within the treated core and often result in coredistortion.

It is, accordingly, an object of this invention to provide a laminatedtube structure in which materials that cannot be secured to themselvesor to other materials may be used to form a spirally-wound laminatedtube structure. Another object of the invention is to provide alaminated tube having spaced-apart inner and outer tube portions formedof strips spirally wound one upon another and secured together, andsandwiched therebetween spirally-wound strips of a material that cannotbe and is not secured either to the layers forming the sandwiched tubeportion or to the inner and outer tube portions. Still another object isto provide a sandwichtype spirally-wound tube in which the sandwichedtube portion is unsecured to the inner and outer tube portions and thelayers or laminations thereof are spirally wound and have overlappingedge portions. A further object of the invention is to provide alaminated tube that is self-adjustable and stress-releasing so thatunequal stresses developed therein in the forming or treating of thetube are eliminated. Additional objects and advantages will appear asthe specification proceeds.

An embodiment of the invention is illustrated in the drawing, in which-Figure 1 is a transverse sectional view; Fig. 2 is a perspective Viewshowing some of the strips in position to be spirally wound to form thetube; and Fig. 3 is a broken longitudinal sectional view showing a tubeas used to provide a bobbin core.

The laminated tube 10 consists of an inner tube portion 11, an outertube portion 12 spaced therefrom, and a central tube portion 13sandwiched between the inner and outer portions 11 and 12. The innerportion 11 is formed by a plurality of spirally-wound strips 14 that arewound so that one edge of each strip abuts the opposite edge of the samestrip. Any number of strips maybe wound one upon another and preferablyeach additional spiral strip winding is staggered so that the joint 15formed by the abutment of the edges of the preceding strip is completelycovered by the subsequent Winding. That is to say, the abutting edges 15of each strip are not in alignment but are offset from each other. Anysuitable material may be used to form the inner tube portion 11 and theparticular material will depend upon the desired physical and electricalcharacteristics that are needed for any particular use. For example, theinner tube portion 11 may be formed by spirally Wind'- ing a pluralityof strips of insulating paper one upon another and preferably the stripsare coated with an adhesive so that the contiguous strips are securedtogether by the adhesive. A water-soluble glue or adhesive may beemployed for this purpose.

' Coaxial with the inner tube portion 11 and wound tightly thereabout isthe central tube portion 13. The central portion 13 is formed of aplurality of strips spirally wound one upon another to form the tubeportion 13. Preferably the strips 16 that are spirally wound to providethe central tube portion 13 are wound so that one edge of the stripoverlaps the opposite edge to form a lapped joint that is indicatedgenerally by the numeral 17. In the illustration given, the edge 18 ofthe strip 16 overlaps the edge 19 of the strip on each successivespiralled turn of the strip.

Any material may be used to form the central tube portion 13, and anynumber of layers may be provided by simply increasing the number ofstrips 16 that are employed and spirally wrapping each strip upon thepreceding one. I prefer to use a plastic material to form the strips 16,and especially desirable is a cast polyester film that isthermo-setting. Moreover, a plastic material of this sort having gooddielectric and temperature characteristics and that is smooth andnon-fibrous has been found to provide excellent results. The electricalproperties of the tube may be varied by increasing and decreasing thenumber of strips 16 of plastic that are wound upon the inner tubeportion 11. The strips 16 though wound one upon another in spiral formare not secured together by adhesive or otherwise and are not secured tothe inner tube portion 11. Winding the strips 16 so that one edgethereof overlaps the opposite edge provides a plurality of spaced-apartlips at the joint 17 that extend laterally from the tube periphery. Itis desirable that each subsequent strip 16 be staggered relative to thepreceding strip so that the lapped edges 17 of each strip are notaligned but rather are oliset from each other. A plastic material havingthe properties set out above and that has been used advantageously forthe strips 16 is sold under the trade name Mylar.

The outer tube portion 12 is formed from a plurality of spirally-woundstrips 20 that are wrapped or wound in an identical manner with thestrips 14 forming the inner tube portion 11. A smooth joint or seam 21is thereby provided and preferably the initial strip 20 contiguous withthe plastic strips 16 is staggered relative thereto so that the lappedseams 17 are completely covered. Similarly, each subsequent strip 2-0 isstaggered relative to the preceding strip so that the smooth seams 21 ofeach strip are not aligned. Any material may be employed for forming theouter tube portion 12, and an adhesive-coated insulating paper may beemployed.

The strips of insulating paper 20 wound one upon another are securedtogether by adhesive, while the initial or inner strip 20 is not securedto the central tube portion 13.

The outer strips 20 are spirally wound tightly about the central tubeportion 13 made of the plastic strips 16. Since no adhesive or othermeans is employed to secure the outer tube portion to the central tubeportion, limited shifting or movement between the tube portions mayresult under certain conditions, while the laterally-extending lips 17provide a relatively sharp edge that tends to bite into the strips ofpaper 20 and to thereby normally hold the inner and outer tube portionsin position relative to each other. In the same manner, the inner tubeportion 12, since it is not secured to the central tube portion 13, mayshift relative thereto, while the joint or seam 17 also provides aninwardly-extending lip having a relatively sharp edge that tends to biteinto the inner tube portion and to lock the inner portion and centraltube portion together.

Normally, the friction between the central tube portion 13 and the innerand outer tube portions 11 and 12 respectively that lie against thesame, and the biting action of the inwardly and outwardly extending lipsprovided by the joints or seams 17, tend to hold the tube portions inpredetermined position. Since the spirallywound strips forming the innerand outer tube portions are secured to the contiguous strips of eachportion by adhesive, a rigid and stable tube structure is provided.However, when the tube 10 is cut into appropriate lengths to provide acore 22 equipped with terminal flanges 23 to provide a bobbin upon whichelectrical transformer windings may be mounted, the heat developed bythe flow of current through the conductor turns does not cause adistortion of the core 22 by amplifying any latent stresses that mayhave developed in forming the tube 10. Instead, a shifting between thetube portions is permissible and a self-adjusting or self-aligning ofthe core portions results that is effective to reduce and substantiallyeliminate the stresses that normally cause core distortion. The sameshifting and self-aligning characteristic results in adjustment of thetube portions relative to each other whenever the tube or core issubjected to treating operations that normally would cause the unequaltube stresses to distort the tube or core during such operation.

The tube structure I have provided is sufficiently strong and rigid toenable its use in customary applications. At the same time, thestructure permits the use of materials such as certain plastics thathave very desirable dielectric and insulating properties but have thedisadvantages of not being susceptible to adhesives and heat sealingmethods, etc., to secure layers of the material to each other or toother, different materials. Yet the tube structure may be formed in aspiral winding operation wherein the rate of tube formation is very highand is therefore desirable commercially.

While in the foregoing specification and embodiment of the invention hasbeen set forth in considerable detail for purposes of illustration, itwill be apparent to those skilled in the art that considerable deviationfrom the details may be made without departing from the spirit of theinvention.

I claim:

1. A laminated tube, comprising a plurality of strips of insulatingmaterial wound one upon another and secured together to form a tubularbase, a plurality of plastic strips wound one upon another coaxial withsaid base and snugly enclosing the same, one edge portion of eachplastic strip being in overlapping relation with the opposite edgeportion of the same strip, and a plurality of strips of insulatingmaterial wound one upon another coaxial with said plastic strips andsnugly enclosing the same, said last-mentioned strips of insulatingmaterial being secured together one upon another, said plastic stripsbeing sandwiched between said base and said last-mentioned strips andbeing maintained in sandwiched relation therebetween solely by thefrictional grip thereof.

2. A laminated tube, comprising a plurality of spirally- Wound strips ofinsulating material, one upon another and adhesively secured together toform a tubular base, a plurality of spirally-wound strips ofthermo-setting plastic, one upon another and all being coaxial with saidbase and snugly enclosing the same, and a plurality of spirally-woundstrips of insulating material coaxial with said plastic strips andsnugly enclosing the same, said last-mentioned strips of insulatingmaterial being adhesively secured together one upon another, said stripsof plastic material being sandwiched between said base and saidlast-mentioned strips but not secured thereto or to each other.

3. A laminated tube adapted for electrical insulating uses, comprising aplurality of spiraled strips, one upon another and all being secured toeach other by adhesive to form a tubular base, a plurality ofthermo-setting plastic strips spirally wound one upon another coaxialwith said base and snugly enclosing-the same, one edge portion of eachstrip of plastic being in overlapping relation with the opposite edgeportion of the same strip to provide laterally-extending lips, and aplurality of spiraled strips coaxial with said plasti strips and snuglyenclosing the same, said last-mentioned strips being secured togetherone upon another by adhesive to form another tube portion, said plasticstrips being sandwiched between said base and said outer tube portionout not secured thereto.

4. The laminated tube according to claim 3 in which said thermo-settingplastic strips are a cast polyester film having relatively highdielectric properties and are rela tively smooth and non-fibrous.

5. A laminated tube structure, comprising a plurality of spirally-woundstrips one upon another and secured together to form a base, a pluralityof spirally-wound strips formed of a material that is resistive toadhesives and heat sealing means as a means for securing the stripstogether, said second-mentioned strips being wound one upon anothercoaxial with said base and snugly enclosing the same, and a plurality ofspirally-wound strips coaxial with said second-mentioned strips andsnugly enclosing the same, said last-mentioned strips being securedtogether one upon another to form an outer tube portion, saidsecondmentioned strips being interposed between said base and outer tubeportion, frictionally engaging each and being unsecured to either and toeach other.

6. A spirally-wound laminated tube, comprising a plu rality ofspirally-wound strips one upon another and all being secured to eachother by adhesive and forming a tubular base, a plurality ofthermo-setting plastic strips spirally wound one upon another coaxialwith said base and snugly enclosing the same, one edge portion of eachstrip of plastic being in overlapping relation with the opposite edgeportion of the same strip to provide laterally-extending lips, saidplastic strips being resistive to adhesive, and a plurality of spiralledstrips coaxial with said plastic strips and snugly enclosing the same,said last-mentioned strips being secured together one upon another byadhesive to form an outer tube portion, said plastic strips beingsandwiched between said base and outer tube portion but not securedthereto or to each other.

7. A laminated tube structure comprising an elongated tubular base, atleast one strip of material spirally wound upon said base andsubstantially covering the same with one spirally Wound edge thereofoverlapping the other spirally wound edge thereof, and at least twostrips of material adapted to be secured to each other, one strip beingspirally wound upon said first mentioned strip and the other beingspirally wound thereover and being secured thereto to form an outer,integrated sheath, said first mentioned strip being sandwiched betweensaid base and sheath and frictionally engaging the same though otherwiseunsecured thereto throughout its entire length.

8. A laminated tube structure comprising an elongated tubular base, anintegral sheath coaxial with said base, and at least one spirally woundstrip interposed between said sheath and said base and being spirallywound upon the latter with the longitudinal edges thereof in overlappingrelation, said last mentioned strip being frictionally engaged by saidsheet and base and being held in position therebetween by the frictionalgrip thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,390,644 Ritchie Sept. 13, 1921 1,495,823 Underhill May 27, 19242,054,769 Holtz Sept. 15, 1936 2,465,257 Nebesar Mar. 22, 1949 2,623,445Robinson Dec. 30, 1952 2,640,501 Scott et a1. June 22, 1953

